Calculating sample size for non-inferiority trial using Stata cii

[kohyle]

Hi, can I use Stata command cii to calculate the sample size required if I want to test that fasting TG is not lower than non-fasting TG by 0.2mmol/l? Given mean=1.4, sd=0.5, 95% confidence level. What is the exact command?

How do I calculate sample size if I want to test for equivalence of the two TGs with the same information?

Thanks!

 

[hlsmith]

Not a regular STATA user, but got following in SAS.




Hmm, if blurry - it said about 5 per group given power .8, alpha .05, etc.

 

[ondansetron]

Not a regular STATA user, but got following in SAS.




Hmm, if blurry - it said about 5 per group given power .8, alpha .05, etc.

Also, remember that sample size calculations are absolutely the minimum number of observations if you used the correct assumptions and if there are no sources of bias or any other issues. This calculation is only "true" under perfect conditions. So, if 5 is the minimum per group, it is probably wise to get more subjects per group, unless there is something extremely prohibitive about that. This gives you room for normal issues that arise and also protects you to an extent from being under powered if you over estimate the effect size or underestimate the variability, for example.

 

[kohyle]

Thanks ondansetron and hlsmith!